Device and method for reproducing information, and computer program

ABSTRACT

An information reproducing apparatus ( 1 ) is provided with: a correcting device ( 18 ) for correcting waveform distortion occurring in a read signal corresponding to a long mark, of a read signal (R RF ) read from a recording medium ( 100 ); and a processing device ( 15 ) for performing a PRML (Partial Response Maximum Likelihood) process on the read signal in which the waveform distortion is corrected

TECHNICAL FIELD

The present invention relates to an information reproducing apparatusand method which reproduce record data recorded on a recording medium,and particularly relates to an information reproducing apparatus andmethod which perform waveform equalization, such as a PRML process, on aread signal obtained by reading the record data recorded on therecording medium, as well as a computer program which makes a computerfunction as the information reproducing apparatus.

BACKGROUND ART

In order to improve the reproduction quality of a read signal read fromthe recording medium on which the data is recorded at high density, apatent document 1 discloses such a technology that a reproduction systemwhich does not require a high-frequency component is realized byapplying a partial response method and by intentionally providingwaveform interference in a reproduction system in which an S/N ratio isincreased and the amplitude of a high-frequency component isdeteriorated with increasing the recording density in a linear recordingdirection, and that a maximum likelihood decoding method is applied bywhich a most probable series is estimated from a probability calculationconsidering the waveform interference (a technology about a so-calledPRML process).

Patent document 1: Japanese Patent Application Laid. Open No. 2005-93033

DISCLOSURE OF INVENTION Subject to be Solved by the Invention

Here, waveform distortion can occur in the read signal. The waveformdistortion indicates such a status that there is a discrepancy between aproper signal level to be taken and a signal level that actually appearsin the read signal. The waveform distortion likely deteriorates thereproduction quality. This likely leads to a disadvantage that a markwith a relatively long run length is misjudged to be another mark.Specifically, for example, this likely leads to a disadvantage that amark with a run length of 8T is misjudged to be a mark with a run lengthof 4T, a space with a run length of 2T, and a mark with a run length of2T.

In view of the aforementioned conventional problems, it is therefore anobject of the present invention to provide an information reproducingapparatus and method which can preferably reproduce the record data evenif the waveform distortion occurs, as well as a computer program.

Means for Solving the Subject

The above object of the present invention can be achieved by aninformation reproducing apparatus provided with: a correcting device forcorrecting waveform distortion occurring in a read signal correspondingto at least a long mark, of a read signal read from a recording medium;and a processing device for performing a PRML (Partial Response MaximumLikelihood) process on the read signal in which the waveform distortionis corrected.

The above object of the present, invention can be also achieved by aninformation reproducing method provided with: a correcting process ofcorrecting waveform distortion occurring in a read signal correspondingto at least a long mark, of a read signal read from a recording medium;and a processing process of performing a PRML (Partial. Response MaximumLikelihood) process on the read signal in which the waveform distortionis corrected.

The above object of the present invention can be also achieved by acomputer program for reproduction control and for controlling a computerprovided in an information reproducing apparatus provided with: acorrecting device for correcting waveform distortion occurring in a readsignal corresponding to at least a long mark, of a read signal read froma recording medium; and a processing device for performing a PRML(Partial Response Maximum. Likelihood) process on the read signal inwhich the waveform distortion is corrected, the computer program makingthe computer function as at least one portion of the correcting deviceand the processing device.

The operation and other advantages of the present invention will becomemore apparent from the embodiments described below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram conceptually showing the basic structure of aninformation reproducing apparatus in an example.

FIG. 2 are waveform charts conceptually showing a first example ofwaveform distortion.

FIG. 3 are waveform charts conceptually showing a second example ofwaveform distortion.

FIG. 4 is a flowchart conceptually showing a flow of an operation ofcorrecting the waveform distortion.

FIG. 5 is a waveform chart conceptually showing the operation ofcorrecting the waveform distortion on the sample value series RS_(C) ifa PRML signal processing circuit adopts a PR(1, 2, 1) method.

FIG. 6 is a waveform chart conceptually showing the operation ofcorrecting the waveform distortion on the sample value series RS_(C) ifthe PRML signal processing circuit adopts a PR(1, 2, 2, 1) method.

FIG. 7 is a waveform chart conceptually showing the operation ofcorrecting the waveform distortion on the sample value series RS_(C) ifthe PRML signal processing circuit adopts a PR(1, 2, 2, 2, 1) method.

FIG. 8 is a waveform chart conceptually showing the operation ofcorrecting the waveform distortion on the sample value series RS_(C) ifthe PRML signal processing circuit adopts a PR(1, 2, 2, 2, 2, 1) method.

FIG. 9 is a waveform chart conceptually showing a waveform or the likeof a read signal before and after the correction of the waveformdistortion.

FIG. 10 is a block diagram conceptually showing the structure of awaveform distortion correction circuit provided for an informationreproducing apparatus in a first modified example.

FIG. 11 is a block diagram conceptually showing the structure of awaveform distortion detection circuit provided for the waveformdistortion correction circuit provided for the information reproducingapparatus in the first modified example.

FIG. 12 is a flowchart conceptually showing a flow of operations by theinformation reproducing apparatus in the first modified example.

FIG. 13 is a timing chart conceptually showing an operation ofcorrecting the waveform distortion by an information reproducingapparatus in a second modified example, on a first read signal.

FIG. 14 is a timing chart conceptually showing the operation ofcorrecting the waveform distortion by the information reproducingapparatus in the second modified example, on a second read signal.

FIG. 15 is a flowchart conceptually showing a first flow of operationsby the information reproducing apparatus in the second modified example.

FIG. 16 is a flowchart conceptually showing a second flow of operationsby the information reproducing apparatus in the second modified example.

FIG. 17 is a flowchart conceptually showing a third flow of operationsby the information reproducing apparatus in the second modified example.

FIG. 18 are a state transition diagram in the PR (1, 2, 2, 1) method anda trellis diagram obtained by developing the state transition diagram ina time axis direction.

FIG. 19 is a waveform diagram conceptually showing the operation ofcorrecting the waveform distortion, on the sample value series, theoperation being aimed at sample values included in a range between asample value located two after a first zero cross point and a samplevalue located two before a second zero cross point, if the PR (1, 2,2, 1) method is applied.

FIG. 20 is a waveform diagram conceptually showing the operation ofcorrecting the waveform distortion, on the sample value series, theoperation being aimed at sample values included in a range between asample value located one after the first zero cross point and a samplevalue located one before the second zero cross point, if the PR (1, 2,2, 1) method is applied.

FIG. 21 is a plan view schematically showing marks on a recordingsurface of a read-only type optical disc.

DESCRIPTION OF REFERENCE CODES

-   1, 2 information reproducing apparatus-   10 spindle motor-   11 pickup-   12 HPF-   13 A/D converter-   14 pre-equalizer-   15 PRML signal processing circuit-   16 binary circuit-   17 decoding circuit-   18 waveform distortion correction circuit-   181 delay adjustment circuit-   182 distortion-correction-value detection circuit-   183 mark/space length detection circuit-   184 timing generation circuit-   185 selector-   186 waveform distortion detection circuit

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, as the best mode for carrying out the present invention, anexplanation will be given on embodiments of the information reproducingapparatus and method, and the computer program of the present invention.

Embodiment of Information Reproducing Apparatus

An embodiment of the information reproducing apparatus of the presentinvention is an information reproducing apparatus provided with: acorrecting device for correcting waveform distortion occurring in a readsignal corresponding to at least a long mark, of a read signal read froma recording medium; and a processing device for performing a PRML(Partial Response Maximum Likelihood) process on the read signal inwhich the waveform distortion is corrected.

According to the embodiment of the information reproducing apparatus ofthe present invention, by the operation of the correcting device, thewaveform distortion is corrected which occurs in the read signalcorresponding to at least the long mark (e.g. marks with run lengths of7T to 11T and 14T if the recording medium is a DVD, and marks with runlengths of 6T to 9T if the recording medium is a Blu-ray Disc). Here,the waveform distortion (and more specifically, for example, the signallevel or the like of the waveform distortion) is preferably correctedsuch that the waveform distortion does not have an adverse effect on thePRML process described later.

Then, by the operation of the processing device, the PRML process isperformed on the read signal in which the waveform distortion iscorrected (hereinafter referred to as a “distortion-corrected signal”,as occasion demands). Incidentally, the PRML process is described in theaforementioned patent document 1 or the like, so that the detailedexplanation thereof will be omitted.

As described above, since the waveform distortion occurring in the readsignal is corrected before the PRML process is performed, the waveformdistortion hardly has or does not have an adverse effect on the PRMLprocess even if the waveform distortion occurs in the read signal readfrom the recording medium. More specifically, for example, it ispossible to preferably prevent such a disadvantage that the long mark ismisjudged to be another mark. By this, the PRML process can bepreferably performed even on the read signal in which the waveformdistortion occurs. As a result, it is possible to preferably reproducethe record data.

In one aspect of the information reproducing apparatus of the presentinvention, if the waveform distortion occurs in a direction that asignal level increases (in other words, if the signal level of thewaveform distortion is greater than a proper signal level to be taken),the correcting device corrects the waveform distortion by correcting asignal component of the read signal which is less than or equal to areference level and which is in a range that does not mislead a pathmetric selection in the PRML process.

According to this aspect, by correcting such a signal component, it ispossible to preferably correct the waveform distortion without having anadverse effect on the PRML process.

Incidentally, the “reference cross point” in the embodiment indicates apoint at which the signal level of the read signal crosses the referencelevel. If the reference level is a zero level, the reference cross pointcorresponds to a zero cross point.

In another aspect of the information reproducing apparatus of thepresent invention, if the waveform distortion occurs in a direction thata signal level reduces (in other words, if the signal level of thewaveform distortion is less than a proper signal level to be taken), thecorrecting device corrects the waveform distortion by correcting asignal component of the read signal which is greater than or equal to areference level and which is in a range that does not mislead a pathmetric selection in the PRML process.

According to this aspect, by correcting such a signal component, it ispossible to preferably correct the waveform distortion without having anadverse effect on the PRML process.

In another aspect of the information reproducing apparatus of thepresent invention, if the processing device adopts a PR (C1, C21, C22,C2k, C1) method, the correcting device corrects the waveform distortionby correcting a signal component between a sample value which appears(k+1)/2 after a first reference cross point and a sample value whichappears (k+1)/2 before a second reference cross point located next tothe first reference cross point.

According to this aspect, by correcting such a signal component,possible to preferably correct the waveform distortion without having anadverse effect on the PRML process.

In another aspect of the information reproducing apparatus of thepresent invention, if the processing device adopts a PR (1, 2, 1)method, the correcting device corrects the waveform distortion bycorrecting a signal component between a sample value which appears oneafter a first reference cross point and a sample value which appears onebefore a second reference cross point located next to the firstreference cross point.

According to this aspect, by correcting such a signal component, it ispossible to preferably correct the waveform distortion without having anadverse effect on the PRML process which adopts the PR (1, 2, 1) method.

In another aspect of the information reproducing apparatus of thepresent invention, if the processing device adopts a PR (1, 2, 2, 1)method, the correcting device corrects the waveform distortion bycorrecting a signal component between a sample value which appears twoafter a first reference cross point and a sample value which appears twobefore a second reference cross point located next to the firstreference cross point.

According to this aspect, by correcting such a signal component, it ispossible to preferably correct the waveform distortion without having anadverse effect on the PRML process which adopts the PR (1, 2, 2, 1)method.

In another aspect information reproducing apparatus of the presentinvention, if the processing device adopts a PR (1, 2, 2, 2, 1) method,the correcting device corrects the waveform distortion by correcting asignal component between a sample value which appears two after a firstreference cross point and a sample value which appears two before asecond reference cross point located next to the first reference crosspoint.

According to this aspect, by correcting such a signal component, it ispossible to preferably correct the waveform distortion without having anadverse effect on the PRML process which adopts the PR (1, 2, 2, 2, 1)method.

In another aspect of the information reproducing apparatus of thepresent invention, if the processing device adopts a PR (1, 2, 2, 2,2, 1) method, the correcting device corrects the waveform distortion bycorrecting a signal component between a sample value which appears threeafter a first reference cross point and a sample value which appearsthree before a second reference cross point located next to the firstreference cross point.

According to this aspect, by correcting such a signal component, it ispossible to preferably correct the waveform distortion without having anadverse effect on the PRML, process which adopts the PR (1, 2, 2, 2,2, 1) method.

In another aspect of the information reproducing apparatus of thepresent invention, if the waveform distortion occurs in a direction thata signal level increases, the correcting device corrects the signallevel of the waveform distortion to a predicated minimum value in thePRML process.

According to this aspect, it is possible to correct the signal level ofthe waveform distortion to a preferable signal level. Namely, it ispossible to preferably correct the waveform distortion.

In another aspect of the information reproducing apparatus of thepresent invention, if the waveform distortion occurs in a direction thata signal level reduces, the correcting device corrects the signal levelof the waveform distortion to a predicated maximum value in the PRMLprocess.

According to this aspect, it is possible to correct the signal level ofthe waveform distortion to a preferable signal level. Namely, it ispossible to preferably correct the waveform distortion.

In another aspect of the information reproducing apparatus of thepresent invention, it is further provided with a detecting device fordetecting the waveform distortion, the correcting device correcting thewaveform distortion if the waveform distortion is detected by thedetecting device.

According to this aspect, the waveform is corrected selectively when thewaveform distortion is detected. Therefore, it is possible to receivethe aforementioned various effects while reducing a load of theinformation reproducing apparatus.

In another aspect of the embodiment of the information reproducingapparatus of the present invention, the correcting device corrects thewaveform distortion (i) if an error correction of the read signal cannotbe performed, (ii) if an error rate of the read signal (and morespecifically, a reading error rate of the record data obtained from theread signal) is greater than or equal to a predetermined thresholdvalue, or (iii) if a read signal corresponding to synchronization datacannot be read, the synchronization data being used to read user dataincluded in record data, the synchronization data being included in therecord data.

According to this aspect, it is possible to receive the aforementionedvarious effects while reducing the load of the information reproducingapparatus by selectively correcting the waveform distortion in theaforementioned cases.

In particular, as opposed to the recording medium which allows onlysequential recording, various recording statuses are mixed in therecording medium which allows random recording. In this case, it isnecessary to read the read signal in which the waveform distortion isdiscontinuously or discretely distributed or not distributed, or to readthe read signal which has various signal levels. Therefore, byreproducing the record data without correcting the waveform distortionin a normal case and by reproducing the record data while selectivelycorrecting the waveform distortion in the aforementioned cases, it ispossible to receive the aforementioned various effects while reducingthe load of the information reproducing apparatus.

In another aspect of the embodiment of the information reproducingapparatus of the present invention, the correcting device corrects thewaveform distortion occurring in the read signal corresponding tosynchronization data, the synchronization data being used to read userdata included in record data, the synchronization data being included inthe record data.

According to this aspect, since at least the read signal correspondingto the synchronization data which is important in reproducing the recorddata can be certainly read, the record data can be preferablyreproduced.

In an aspect of the information reproducing apparatus in which thewaveform distortion occurring in the read signal corresponding to thesynchronization data is corrected, as described above, the correctingdevice may correct the waveform distortion at least one of before aspace which makes a pair with a mark which constitutes thesynchronization data of the read signal, after the space, and at aposition which satisfies periodicity of the synchronization data, with abase point at the space. Specifically, for example, if the recordingmedium is a Blu-ray Disc, the correcting device may detect a space witha run length of 9T which makes a pair with a mark with a run length of9T which constitutes the synchronization data and may correct thewaveform distortion at least one of before and after the space with arun length of 9T. Alternatively focusing on the periodicity of thesynchronization data, the correcting device may correct the waveformdistortion near a position after a lapse of a time corresponding to1932T from the space with a run length of 9T. Alternatively, forexample, if the recording medium is a DVD, focusing on the periodicityof the synchronization data, the correcting device may correct thewaveform distortion near a position after a lapse of a timecorresponding to 1488T from a space with a run length of 14T.

By virtue of such construction, focusing on the periodicity that thesynchronization data appears, it is possible to correct the waveformdistortion in the read signal corresponding to the synchronization data,relatively easily.

In another aspect of the embodiment of the information reproducingapparatus of the present invention, the long mark is a mark whose signallevel is maximum amplitude.

According to this aspect, it is possible to preferably correct thewaveform distortion occurring in the read signal corresponding to thelong mark.

In another aspect of the embodiment of the information reproducingapparatus of the present invention, the processing device is providedwith: an equalizing device for partial-response equalizing the readsignal on the basis of intentional waveform interference which can limitan area frequency component included in the read signal; and a MaximumLikelihood decoding device for estimating a most probable series withrespect to an output of said equalizing device.

According to this aspect, by the operations of the equalizing device andthe Maximum Likelihood decoding device, it is possible to preferablyperform the PRML process on the read signal in which the waveformdistortion is corrected.

Embodiment of Information Reproducing Method

An embodiment of the information reproducing method of the presentinvention is an information reproducing method provided with: acorrecting process of correcting waveform distortion occurring in a readsignal corresponding to at least a long mark, of a read signal read froma recording medium; and a processing process of performing a PRML(Partial Response Maximum Likelihood) process on the read signal inwhich the waveform distortion is corrected.

According to the embodiment of the information reproducing method of thepresent invention, it is possible to receive the same various effects asthose that can be received by the aforementioned embodiment of theinformation reproducing apparatus of the present invention.

Incidentally, in response to the various aspects in the aforementionedembodiment of the information reproducing apparatus of the presentinvention, the embodiment of the information reproducing method of thepresent invention can also adopt various aspects.

Embodiment of Computer Program

An embodiment of the computer program of the present invention is acomputer program for reproduction control and for controlling a computerprovided in an information reproducing apparatus provided with: acorrecting device for correcting waveform distortion occurring in a readsignal corresponding to at least a long mark, of a read signal read froma recording medium; and a processing device for performing a PRML(Partial Response Maximum Likelihood) process on the read signal inwhich the waveform distortion is corrected (i.e. the embodiment of theinformation reproducing apparatus of the present invention (includingits various aspects)), the computer program making the computer functionas at least one portion of the correcting device and the processingdevice.

According to the embodiment of the computer program of the presentinvention, the aforementioned embodiment of the information reproducingapparatus of the present invention can be relatively easily realized asa computer reads and executes the computer program from a programstorage device, such as a ROM, a CD-ROM, a DVD-ROM, and a hard disk, oras it executes the computer program after downloading the programthrough a communication device.

Incidentally, in response to the various aspects in the aforementionedembodiment of the information reproducing apparatus of the presentinvention, the embodiment of the computer program of the presentinvention can also employ various aspects.

An embodiment of the computer program product of the present inventionis a computer program product in a computer-readable medium for tangiblyembodying a program of instructions executable by a computer provided inan information reproducing apparatus provided with: a correcting devicefor correcting waveform distortion occurring in a read signalcorresponding to at least a long mark, of a read signal read from arecording medium; and a processing device for performing a PRML (PartialResponse Maximum Likelihood) process on the read signal in which thewaveform distortion is corrected (i.e. the embodiment of the informationreproducing apparatus of the present invention (including its variousaspects)), the computer program making the computer function as at leastone portion of the correcting device and the processing device.

According to the embodiment of the computer program product of thepresent invention, the aforementioned embodiment of the informationreproducing apparatus of the present invention can be embodiedrelatively readily, by loading the computer program product from arecording medium for storing the computer program product, such as a ROM(Read Only Memory), a CD-ROM (Compact Disc-Read Only Memory), a DVD-ROM(DVD Read Only Memory), a hard disk or the like, into the computer, orby downloading the computer program product, which may be a carrierwave, into the computer via a communication device. More specifically,the computer program product may include computer readable codes tocause the computer (or may comprise computer readable instructions forcausing the computer) to function as the aforementioned embodiment ofthe information reproducing apparatus of the present invention.

Incidentally, in response to the various aspects in the aforementionedembodiment of the information reproducing apparatus of the presentinvention, the embodiment of the computer program product of the presentinvention can also employ various aspects.

The operation and other advantages of the present invention will becomemore apparent from the examples explained below.

As explained above, according to the embodiment of the informationreproducing apparatus of the present invention, it is provided with thecorrecting device and the processing device. According to the embodimentof the information reproducing method of the present invention, it isprovided with the correcting process and the processing process.According to the embodiment of the computer program of the presentinvention, it makes a computer function as the embodiment of theinformation reproducing apparatus of the present invention. Therefore,it is possible to preferably reproduce the data even if the waveformdistortion occurs.

EXAMPLES

Hereinafter, an example of the present invention will be described onthe basis of the drawings.

(1) Basic Structure

Firstly, with reference to FIG. 1, an example of the informationreproducing apparatus of the present invention will be described. FIG. 1is a block diagram conceptually showing the basic structure of theinformation reproducing apparatus in the example.

As shown in FIG. 1, an information reproducing apparatus 1 in theexample is provided with a spindle motor 10, a pickup (PU) 11, a HPF(High Pass Filter) 12, an A/D converter 13, a pre-equalizer 14, a RPMLsignal processing circuit 15, a decoding circuit 17, and a waveformdistortion correction circuit 18.

The pickup 11 photoelectrically converts reflected light when a laserbeam LB is irradiated to a recording surface of an optical disc 100rotated by the spindle motor 10, thereby generating a read signalR_(RF).

The HPF 12 removes a low-frequency component of the read signal R_(RF)outputted from the pickup, and it outputs a resulting read signal R_(HC)to the A/D converter 13.

The A/D converter 13 samples the read signal in accordance with asampling clock outputted from a PLL (Phased Lock Loop) not illustratedor the like, and it outputs a resulting read sample value series RS tothe pre-equalizer 14.

The pre-equalizer 14 removes intersymbol interference which is based ontransmission characteristics in an information reading system, which isformed of the pickup 11 and the optical disc 100, and it outputs aresulting read sample value series RS_(C) to the waveform distortioncorrection circuit 18.

The waveform distortion correction circuit 18 constitutes one specificexample of the “correcting device” of the present invention. Thewaveform distortion correction circuit 18 corrects waveform distortionoccurring in the read sample value series RS_(C) (i.e. waveformdistortion occurring in the read signal R_(RF)). A resultingdistortion-corrected read sample value series RS_(CAM) is outputted tothe PRML signal processing circuit 15.

The PRML signal processing circuit 15 performs a PRML process on thedistortion-corrected read sample value series RS_(CAM), and it outputs aresulting binary signal to the decoding circuit 17.

Incidentally, the PRML signal processing circuit 15 is provided with aPR (Partial Response) equalization circuit 151, represented by a FIR(Finite Impulse Response) filter, a transversal filter, or the like; anda maximum likelihood decoding circuit 152 represented by Viterbi decoderor the like. The PR equalization circuit 15 performs a partial responseequalization process for limiting or controlling a high-frequency noiseand providing intentional intersymbol interference, on thedistortion-corrected read sample value series RS_(CAM). The maximumlikelihood decoding circuit 152 estimates a most probable series, on thebasis of an added coding rule, with respect to the distortion-correctedread sample value series RS_(CAM) on which the partial responseequalization process is performed, thus generating the binary signal.Such a PRML process can use a conventional PRML process, so that thedetailed explanation thereof will be omitted.

The decoding circuit 17 performs a decoding process or the like on thebinary signal, and it outputs a resulting reproduction signal toexternal reproduction equipment, such as a display and a speaker. As aresult, data recorded on the optical disc 100 (e.g. video data, audiodata, and the like) is reproduced.

In the information reproducing apparatus 1 in the example, inparticular, the PRML process is performed on the PRML signal processingcircuit 15 after the correction of the waveform distortion. Hereinafter,specific examples of the correction of the waveform distortion will bedetailed.

(2) Waveform Distortion

Firstly, with reference to FIG. 2 and FIG. 3, the waveform distortionwill be described. FIG. 2 are waveform charts conceptually showing afirst example of waveform distortion. FIG. 3 are waveform chartsconceptually showing a second example of waveform distortion.

As shown in FIG. 2( a), the waveform distortion indicates a differencebetween a proper signal level to be taken and a signal level thatactually appears in the read signal R_(RF). The waveform distortion isquantitatively defined by a waveform distortion amount D for the maximumamplitude A of the read signal R_(RF), and a waveform distortion amountD′ which is a signal level from a zero level to the peak of the waveformdistortion. In FIG. 2( a), a thick dashed line denotes the proper signallevel to be taken when there is no waveform distortion. If there is nowaveform distortion, the waveform distortion amount D is obviously zero.

Incidentally, the waveform distortion shown in FIG. 2( a) shows suchwaveform distortion that the signal level in a middle portion ischanged, compared to the signal level in a front edge portion and a rearedge portion of the read signal R_(RF). Apart from such waveformdistortion, there can be such waveform distortion that the signal levelin the front edge portion and the middle portion is changed, compared tothe signal level in the rear edge portion of the read signal R_(RF) asshown in FIG. 2( b); and such waveform distortion that the signal levelin the middle edge portion and the rear portion is changed, compared tothe signal level in the front edge portion of the read signal R_(RF) asshown in FIG. 2( c). For any waveform distortion, the structure andoperation described later can be obviously adopted.

Moreover, in FIG. 2( a) to FIG. 2( c), an explanation was given on thewaveform distortion occurring on the optical disc 100 in which thereflectance of the laser beam LB is reduced by forming the marks. Inother words, an explanation was given on the example in which thewaveform distortion occurs such that the signal level unintentionallyincreases in the signal level which is the zero level or less. However,as shown in FIG. 3( a), there can be also the waveform distortionoccurring on the optical disc 100 (or so-called low-to-high disc) inwhich the reflectance of the laser beam LB is increased by recording thedata, as in an optical disc such as a Blu-ray disc in which a pigmentedfilm is used as a recording layer. In other words, such waveformdistortion can occur that the signal level unintentionally reduces inthe signal level which is the zero level or more. Incidentally, in thecase where such waveform distortion can occur that the signal levelunintentionally reduces in the signal level which is the zero level ormore, there can be such waveform distortion that the signal level in thefront edge portion and the middle portion is changed, compared to thesignal level in the rear edge portion of the read signal R_(RF), asshown in FIG. 3( b), as in the case where such waveform distortionoccurs that the signal level unintentionally reduces as shown in FIG. 2(b), in the signal level which is the zero level or more. Moreover, therecan be also such waveform distortion that the signal level in the middleportion and the rear edge portion is changed, compared to the signallevel in the front edge portion of the read signal R_(RF), as shown inFIG. 3( c), as in the case where such waveform distortion occurs thatthe signal level unintentionally reduces shown in FIG. 2( c).

Moreover, in the example, it is preferable to focus on the waveformdistortion which occurs in the read signal corresponding to the recordmark with a relatively long run length (hereinafter referred to as a“long mark”: e.g. data with run lengths of 7T to 11T or 14T if theoptical disc 100 is a DVD, and data with run lengths of 6T to 9T if theoptical disc 100 is a Blu-ray Disc). Alternatively, with emphasis on theimportance of synchronization data (i.e. sync data), it is preferable tofocus on the waveform distortion which occurs in the read signalcorresponding to the mark corresponding to the synchronization data(e.g. data with a run length of 14T if the optical disc 100 is a DVD,and data with a run length of 9T if the optical disc 100 is a Blu-rayDisc).

(3) Operation Example of Correcting Waveform Distortion

Next, with reference to FIG. 4, an explanation will be given on aspecific operation example of correcting the waveform distortion. FIG. 4is a flowchart conceptually showing a flow of the operation ofcorrecting the waveform distortion.

As shown in FIG. 4, firstly, an operation of reproducing data recordedon the optical disc 100 is performed (step S101).

In the reproduction operation, it is sequentially judged whether or nota symbol error rate (SER) is greater than or equal to a predeterminedthreshold value, or whether or not error correction using an ECC (ErrorCorrection Code) or the like is unable to be performed, or whether ornot the synchronization data is unable to be read (step S102). Here, thepredetermined threshold value is preferably set on the basis of whetheror not the preferable reproduction is performed. Specifically, it ispreferable to set the value of the symbol error rate which does notallow the preferable reproduction operation (e.g. approximately 0.001 ormore), as the predetermined threshold value.

As a result of the judgment in the step S102, if it is judged that thesymbol error rate is not greater than or equal to the threshold value,and that the error correction is not unable to be performed, and thatthe synchronization data is not unable to be read (the step S102: No),the operational flow goes to a step S107.

On the other hand, as a result of the judgment in the step S102, if itis judged that the symbol error rate is greater than or equal to thethreshold value, or that the error correction is unable to be performed,or that the synchronization data is unable to be read (the step S102:Yes), then, the waveform distortion of the long mark is measured (stepS103). Here, a waveform distortion ratio (i.e. D/A×100) which indicatesa ratio of the waveform distortion amount D (or D′) to the maximumamplitude A of the read signal R_(RF).

Then, it is judged whether or not the waveform distortion is greaterthan or equal to a predetermined value (step S104). For example, it isjudged whether or not the waveform distortion ratio is greater than orequal to approximately 30%.

As a result of the judgment in the step S104, if it is judged that thewaveform distortion is not greater than or equal to the predeterminedvalue (e.g. that the waveform distortion ratio is less than or equal toapproximately 30%) (the step S104: No), the operational flow goes to thestep S107.

On the other hand, as a result of the judgment in the step S104, if itis judged that the waveform distortion is greater than or equal to thepredetermined value (e.g. that the waveform distortion ratio is greaterthan or equal to approximately 30%) (the step S104: Yes), then, awaveform distortion correction condition, such as a correction level anda correction range for the waveform distortion, is set (step S105). Thewaveform distortion correction condition will be detailed later (referto FIG. 5 and the like).

Then, the waveform distortion of the long mark is corrected on the basisof the waveform distortion correction condition set in the step S105(step S106). Incidentally, the operation of correcting the waveformdistortion needs to be performed so as not to have an adverse effect ona path metric calculation in the PRML process performed on the PRMLsignal processing circuit 15, as detailed later.

Then, it is judged whether or not the reproduction operation is to beended (step S107), and if the reproduction operation is not to be ended(the step S107: No), the operational flow returns to the step S101, andthe operations after the step S101 are repeated again.

The operation of correcting the waveform distortion described above willbe more clearly explained on waveform charts which show the sample valueseries RS_(C) with reference to FIG. 5 to FIG. 8. FIG. 5 is a waveformchart conceptually showing the operation of correcting the waveformdistortion on the sample value series RS_(C) if the PRML signalprocessing circuit 15 adopts a PR(1, 2, 1) method. FIG. 6 is a waveformchart conceptually showing the operation of correcting the waveformdistortion on the sample value series RS_(C) if the PRML signalprocessing circuit 15 adopts a PR(1, 2, 2, 1) method, FIG. 7 is awaveform chart conceptually showing the operation of correcting thewaveform distortion on the sample value series RS_(C) if the PRML signalprocessing circuit 15 adopts a PR(1, 2, 2, 2, 1) method. FIG. 8 is awaveform chart conceptually showing the operation of correcting thewaveform distortion on the sample value series RS_(C) if the PRML signalprocessing circuit 15 adopts a PR(1, 2, 2, 2, 2, 1) method.

As shown in FIG. 5, if the PRML signal processing circuit 15 adopts aPR(1, 2, 1) method, interpolated sample values, on which the partialresponse equalization is performed, are divided into five values ofRef_H, Ref_L, 0 (ZL: Zero Level), −Ref_and −Ref_H (however, if theshortest mark/space has a run length restriction of 2T or more, they aredivided into the four values except 0). Here, it is correct (i.e. mostprobable) that the interpolated sample value Sip(k) is −Ref_H. Thus, inorder to correct the waveform distortion so as not to influence the pathmetric calculation in the PRML process, the operation of correcting thewaveform distortion is preferably performed in a range between a samplevalue S(k−0.5), which is a sample value located one after a first zerocross point S(k−1.5), and a sample value S(k+5.5), which is a samplevalue located one before a second zero cross point S(k+6.5) located nextto the first zero cross point S(k−1.5). Moreover, the operation ofcorrecting the waveform distortion is preferably performed such that thesignal level after the correction has a predicted minimum value (i.e.−Ref_H) in the PRML process. In conclusion, if the PRML signalprocessing circuit 15 adopts the PR(1, 2, 1) method, the operation ofcorrecting the waveform distortion is preferably performed such that thesignal levels of sample values (i.e. S(k−0.5), S(k+0.5), S(k+1.5),S(k+2.5), S(k+3.5), S(k+4.5), and S(k+5.5)) included in the rangebetween the sample value S(k−0.5) located one after the first zero crosspoint S(k−1.5) and the sample value S(k+5.5) located one before thesecond zero cross point S(k+6.5) have the predicted minimum value (i.e.−Ref_H) in the PRML process.

As shown in FIG. 6, if the PRML signal processing circuit 15 adopts aPR(1, 2, 2, 1) method, interpolated sample values, on which the partialresponse equalization is performed, are divided into seven values ofRef_H, Ref_M, Ref_L, 0 (ZL: Zero Level), −Ref_L, −Ref_M, and −Ref_H.Here, as in the case where the PRML signal processing circuit 15 adoptsthe PR(1, 2, 1) method, if the signal level of the sample value S(k)located one after the first zero cross point S(k−1) is corrected to thepredicted minimum value (−Ref_H), that has an adverse affect on the pathmetric calculation in the PRML process. In the same manner, if thesignal level of the sample value S(k+6) located one before the secondzero cross point S(k+7) is corrected to the predicted minimum value(−Ref_H), that has an adverse affect on the path metric calculation inthe PRML process. Therefore, if the PRML signal processing circuit 15adopts the PR(1, 2, 2, 1) method, the operation of correcting thewaveform distortion is preferably performed such that the signal levelsof sample values (i.e. S(k+1), S(k+2), S(k+3), S(k+4), and S(k+5))included in the range between the sample value S(k+1) located two afterthe first zero cross point S(k−1) and the sample value S(k+5) locatedtwo before the second zero cross point S(k+7) have the predicted minimumvalue (i.e. −Ref_H) in the PRML process.

As shown in FIG. 7, if the PRML signal processing circuit 15 adopts aPR(1, 2, 2, 2, 1) method, interpolated sample values, on which thepartial response equalization is performed, are divided into nine valuesof Ref_H, Ref_MH, Ref_ML, Ref_L, 0 (ZL: Zero Level), −Ref_L, −Ref_ML,−Ref_MH, and −Ref_H. Here, as in the case where the PRML signalprocessing circuit 15 adopts the PR(1, 2, 2, 1) method, even if thesignal level of the sample value S(k+1) located two after the first zerocross point S(k−1) is corrected to the predicted minimum value (−Ref_H),that does not have an adverse affect on the path metric calculation inthe PRML process. In the same manner, even if the signal level of thesample value S(k+5) located two before the second zero cross pointS(k+7) is corrected to the predicted minimum value (−Ref_H), that doesnot have an adverse affect on the path metric calculation in the PRMLprocess. Therefore, if the PRML signal processing circuit 15 adopts thePR(1, 2, 2, 2, 1) method, the operation of correcting the waveformdistortion is preferably performed such that the signal levels of samplevalues (i.e. S(k+1), S(k+2), S(k+3), S(k+4), and S(k+5)) included in therange between the sample value S(k+1) located two after the first zerocross point S(k−1) and the sample value S(k+5) located two before thesecond zero cross point S(k+7) have the predicted minimum value (i.e.−Ref_H) in the PRML process.

As shown in FIG. 8, if the PRML signal processing circuit 15 adopts aPR(1, 2, 2, 2, 2, 1) method, interpolated sample values, on which thepartial response equalization is performed, are divided into elevenvalues of Ref_H, Ref_MH, Ref_MM, Ref_ML, Ref_L, 0 (ZL: Zero Level),−Ref_L, −Ref_ML, −Ref_MM, −Ref_MH, and −Ref_H. Here, as in the casewhere the PRML signal processing circuit 15 adopts the PR(1, 2, 2, 2, 1)method, if the signal level of the sample value S(k+1) located two afterthe first zero cross point S(k−1) is corrected to the predicted minimumvalue (−Ref_H), that has an adverse affect on the path metriccalculation in the PRML process. In the same manner, if the signal levelof the sample value S(k+5) located two before the second zero crosspoint S(k+7) is corrected to the predicted minimum value (−Ref_H), thathas an adverse affect on the path metric calculation in the PRMLprocess. Therefore, if the PRML signal processing circuit 15 adopts thePR(1, 2, 2, 2, 2, 1) method, the operation of correcting the waveformdistortion is preferably performed such that the signal levels of samplevalues (i.e. S(k+2), S(k+3), and S(k+4)) included in the range betweenthe sample value S(k+2) located three after the first zero cross pointS(k−1) and the sample value S(k+4) located three before the second zerocross point S(k+7) have the predicted minimum value (i.e. −Ref_H) in thePRML process.

In conclusion, the following relation can be found. If the PRML signalprocessing circuit 15 adopts the PR(1, 2, . . . , 2, 1) method (wherein2 continues m times), the operation of correcting the waveformdistortion is preferably performed such that the signal levels of samplevalues included in the range between the sample value located (m+1)/2after the first zero cross point and the sample value located (m+1)/2before the second zero cross point have the predicted minimum value inthe PRML process.

Incidentally, the waveform distortion correction condition set in thestep S105 in FIG. 4 corresponds to the signal level after the correction(which corresponds to the predicted minimum value here) and the range(i.e. timing) to perform the operation of correcting the waveformdistortion, explained in FIG. 5 to FIG. 8.

An effect obtained by correcting the waveform distortion will bedescribed with reference to FIG. 9. FIG. 9 is a waveform chartconceptually showing a waveform or the like of the read signal R_(RF)before and after the correction of the waveform distortion.

As shown on the left side of FIG. 9, if the waveform distortion occursin the read signal R_(RF), the waveform distortion is likely misjudgedto be the normal mark (e.g. the mark with a relatively short runlength). Therefore, the binary waveform after binarizing the read signalR_(RF) includes an error signal caused by the waveform distortion. Thisresults in inconsistency with the original record data and causes abinary error.

On the other hand, as shown on the right side of FIG. 9, if the waveformdistortion occurring in the read signal R_(RF) is corrected, the binarywaveform after binarizing the read signal R_(RF) no longer includes theerror signal caused by the waveform distortion. This results inconsistency with the original record data and does not cause the binaryerror.

As explained above, according to the information reproducing apparatus 1in the example, by performing the PRML process, it is possible toreproduce the record data, stably and accurately.

In particular, according to the information reproducing apparatus 1 inthe example, the PRML process is performed on the PRML signal processingcircuit after the correction of the waveform distortion. Thus, forexample, it is possible to preferably prevent such a disadvantage thatthe mark with a relatively long run length is misjudged to be anothermark. As a result, the waveform distortion rarely causes the binaryerror, and this allows the preferable reproduction operation.

Incidentally, in the aforementioned explanation, the zero cross point isused; however, if a reference level is used instead of the zero level,the “zero cross point” is obviously replaced by a “reference crosspoint”.

(4) Modified Examples

Next, with reference to FIG. 10 to FIG. 17, an explanation will be givenon modified examples of the information reproducing apparatus 1 in theexample.

(4-1) First Modified Example

Firstly, with reference to FIG. 10 and FIG. 12, an informationreproducing apparatus 1 a in a first modified example will be described.FIG. 10 is a block diagram conceptually showing the structure of awaveform distortion correction circuit 18 a provided for an informationreproducing apparatus 1 a in a first modified example. FIG. 11 is ablock diagram conceptually showing the structure of a waveformdistortion detection circuit 186 a provided for the waveform distortioncorrection circuit 18 a provided for the information reproducingapparatus 1 a in the first modified example. FIG. 12 is a flowchartconceptually showing a flow of operations by the information reproducingapparatus 1 a in the first modified example.

In the operation example shown in FIG. 4, the waveform distortion isalways corrected if the read signal R_(RF) does not satisfy a desiredreproduction property. In the first modified example, however, even ifthe read signal R_(RF) does not satisfy the desired reproductionproperty, the waveform distortion is corrected selectively when thewaveform distortion is actually detected. Hereinafter, the specificstructure and operation example of the first modified example will bedescribed.

As shown in FIG. 10, the waveform distortion correction circuit 18 a isprovided with a delay adjustment circuit 181 a, a waveform distortiondetection circuit 186 a, a mark/space length detection circuit 183 a, atiming generation circuit 184 a, a selector 185 a, and an AND circuit187 a.

The read sample value series RS_(C) outputted from the pre-equalizer 14is outputted to each of the delay adjustment circuit 181 a, the waveformdistortion detection circuit 186 a, and the mark/space length detectioncircuit 183 a.

The delay adjustment circuit 181 a sets a delay amount corresponding tothe longest run length of the record data and outputs the read samplevalue series RS_(C) to the selector 185 a in desired timing.Specifically, if the optical disc 100 is a Blu-ray Disc, the delayadjustment circuit 181 a sets a delay amount corresponding to thelongest run length of 9T, and if the optical disc 100 is a DVD, thedelay adjustment circuit 181 a sets a delay amount corresponding to thelongest run length of 14T.

The mark/space length detection circuit 183 a detects a mark/spacelength by detecting an interval between the zero cross points, thenumber of continuous coded bits, and the like. The detection result isoutputted to the timing generation circuit 184 a.

The timing generation circuit 184 a generates a timing signal SW on thebasis of the mark/space length detected on the mark/space lengthdetection circuit 183 a and outputs the generated timing signal SW tothe AND circuit 187 a.

Specifically, the timing generation circuit 184 a generates a high-leveltiming signal SW (SW=1) (i) if the mark/space length detected on themark/space length detection circuit 183 a is the long mark which is atarget of the waveform distortion correction and (ii) in a period toinput sample values in a range between the sample value located (m+1)/2after the first zero cross point and the sample value located (m+1)/2before the second zero cross point, and the timing generation circuit184 a outputs the generated timing signal SW to the AND circuit 187 a.On the other hand, the timing generation circuit 184 generates alow-level timing signal SW (SW=0) (i) if the mark/space length detectedon the mark/space length detection circuit 183 a is a mark other thanthe long mark which is a target of the waveform distortion correction or(ii) in a period to input sample values out of the range between thesample value located (m+1)/2 after the first zero cross point and thesample value located (m+1)/2 before the second zero cross point, and thetiming generation circuit 184 a outputs the generated timing signal SWto the AND circuit 187 a.

The waveform distortion detection circuit 186 a detects the waveformdistortion and outputs a waveform distortion detection signal DT whichindicates that the waveform distortion is detected, to the AND circuit187 a. More specifically, the waveform distortion detection circuit 186a outputs a high-level waveform distortion detection signal DT (DT=1) tothe AND circuit 187 a if the waveform distortion is detected, andoutputs a low-level waveform distortion detection signal DT (DT=0) tothe AND circuit 187 a if the waveform distortion is not detected.

The AND circuit 187 a generates a high-level timing signal SW0 if thewaveform distortion is detected (if each of the timing signal. SWoutputted from the timing generation circuit 184 a and the waveformdistortion detection signal DT outputted from the waveform distortiondetection circuit 186 a is high-level), on the basis of the output ofeach of the timing generation circuit 184 a and the waveform distortiondetection circuit 186 a. On the other hand, the AND circuit 187 agenerates a low-level timing signal SW0 if the waveform distortion isnot detected (if either the timing signal SW outputted from the timinggeneration circuit 184 a or the waveform distortion detection signal DToutputted from the waveform distortion detection circuit 186 a islow-level), on the basis of the output of each of the timing generationcircuit 184 a and the waveform distortion detection circuit 186 a. Inother words, in the first modified example, the waveform distortion iscorrected selectively when the waveform distortion is detected.

If the high-level timing signal SW0 is outputted from the AND circuit187 a, the selector 185 a outputs the predicted minimum value (i.e.−Ref_H) outputted from the PRML signal processing circuit 15 as thedistortion-corrected read sample value series RS_(CAM) to the PRMLsignal processing circuit 15. On the other hand, if the low-level timingsignal SW0 is outputted from the AND circuit 187 a, the selector 185 aoutputs the read sample value series RS_(C) outputted from the delayadjustment circuit 181 a as the distortion-corrected read sample valueseries RS_(CAM) to the PRML signal processing circuit 15.

As shown in FIG. 11, the waveform distortion detection circuit 186 a isprovided with a shift register 1831 a, a selector 1832 a, a maximumvalue detection circuit 1833 a, a minimum value detection circuit 1834a, a subtracter 1835 a, and a judgment circuit 1836 a.

The read sample value series RS_(C) inputted to the waveform distortiondetection circuit 186 a is outputted to the shift register 1831 a. Theshift register 1831 a outputs the inputted read sample value seriesRS_(C) to the selector 1832 a as outputs D0 to D14 while shifting theinputted read sample value series RS_(C) by one clock.

The selector 1832 a selectively samples and holds three outputs fromamong the outputs D0 to D14, on the basis of the mark/space length, intiming outputted from the mark/space length detection circuit 183 a, andoutputs the three outputs to the maximum value detection circuit 1833 aand the minimum value detection circuit 1834 a, respectively.

More specifically, the selector 1832 a selectively samples and holdsthree outputs D2, D3, and D4 from among the outputs D0 to D14 if themark/space length outputted from the mark/space length detection circuit183 a is 6T, and outputs the three outputs to the maximum valuedetection circuit 1833 a and the minimum value detection circuit 1834 a,respectively. The selector 1832 a selectively samples and holds threeoutputs D2, D3, and D5 from among the outputs D0 to D14 if themark/space length outputted from the mark/space length detection circuit183 a is 7T, and outputs the three outputs to the maximum valuedetection circuit 1833 a and the minimum value detection circuit 1834 a,respectively. The selector 1832 a selectively samples and holds threeoutputs D2, D4, and D6 from among the outputs D0 to D14 if themark/space length outputted from the mark/space length detection circuit183 a is 8T, and outputs the three outputs to the maximum valuedetection circuit 1833 a and the minimum value detection circuit 1834 a,respectively. The selector 1832 a selectively samples and holds threeoutputs D2, D4, and D7 from among the outputs D0 to D14 if themark/space length outputted from the mark/space length detection circuit183 a is 9T, and outputs the three outputs to the maximum valuedetection circuit 1833 a and the minimum value detection circuit 1834 a,respectively. The selector 1832 a selectively samples and holds threeoutputs D2, D5, and D8 from among the outputs D0 to D14 if themark/space length outputted from the mark/space length detection circuit183 a is 10T, and outputs the three outputs to the maximum valuedetection circuit 1833 a and the minimum value detection circuit 1834 a,respectively. The selector 1832 a selectively samples and holds threeoutputs D2, D5, and D9 from among the outputs D0 to D14 if themark/space length outputted from the mark/space length detection circuit183 a is 11T, and outputs the three outputs to the maximum valuedetection circuit 1833 a, and the minimum value detection circuit 1834a, respectively The selector 1832 a selectively samples and holds threeoutputs D2, D7, and D12 from among the outputs D0 to D14 if themark/space length outputted from the mark/space length detection circuit183 a is 14T, and outputs the three outputs to the maximum valuedetection circuit 1833 a, and the minimum value detection circuit 1834a, respectively. The operation of the selector 1832 a described abovesubstantially corresponds to the operation of selectively outputting thesignal level in the front edge portion, the signal level in the middleportion, and the signal level in the rear edge portion of the waveformdistortion, shown in FIG. 2( a) to FIG. 2( c) and FIG. 3( a) to FIG. 3(c).

Then, on the maximum value detection circuit 1833 a, the maximum value(i.e. the maximum signal level) of the three outputs outputted from theselector 1832 a is detected, and the detected maximum value is outputtedto the subtracter 1835 a.

Moreover, on the minimum value detection circuit 1834 a, the minimumvalue (i.e. the minimum signal level) of the three outputs outputtedfrom the selector 1832 a is detected, and the detected minimum value isoutputted to the subtracter 1835 a.

Then, on the subtracter 1835 a, the minimum value detected on theminimum value detection circuit 1834 a is subtracted from the maximumvalue detected on the maximum value detection circuit 1833 a, by whichthe waveform distortion amount D is calculated.

Then, on the judgment circuit 1836 a, it is judged whether or not thewaveform distortion amount outputted from the subtracter 1835 a isgreater than or equal to a predetermined value x. If the waveformdistortion amount D is relatively small, the waveform distortion is notregarded as being detected, and the low-level waveform distortiondetection signal DT is outputted. On the other hand, if the waveformdistortion amount D is relatively large (e.g. if the waveform distortionratio is greater than or equal to approximately 30%), the waveformdistortion is regarded as being detected, and the high-level waveformdistortion detection signal. DT is outputted.

In a flow of operations at this time, as shown in FIG. 12, firstly, theoperation of reproducing data recorded on the optical disc 100 isperformed (step S101). In the reproduction operation, it is judgedwhether or not the read signal R_(RF) satisfies a desired reproductionproperty (step S102).

As a result of the judgment in the step S102, if it is judged that theread signal R_(RF) satisfies the desired reproduction property (the stepS102: Yes), the operational flow goes to a step S107.

On the other hand, as a result of the judgment in the step S102, if itis judged that the read signal R_(RF) does not satisfy the desiredreproduction property (the step S102: No), then it is judged whether ornot the waveform distortion is actually detected on the waveformdistortion detection circuit 186 a (step S201).

As a result of the judgment in the step S201, if it is judged that thewaveform distortion is not actually detected on the waveform distortiondetection circuit 186 a (the step S201: No), the operational flow goesto the step S107 without correcting the waveform distortion (i.e.without performing the operations in the step S103 to the step S106).

On the other hand, as a result of the judgment in the step S201, if itis judged that the waveform distortion is detected (the step S201: Yes),the operational flow goes to the step S107 after correcting the waveformdistortion (i.e. after performing the operations in the step S103 to thestep S106).

As described above, by selectively correcting the waveform distortionwhen the waveform distortion is detected, it is possible to receive theaforementioned various effects while reducing the load of theinformation reproducing apparatus 1 a.

In addition, the waveform distortion is selectively corrected by thewaveform distortion correction circuit 18 when the waveform distortionactually occurs. Here, in particular, as opposed to the optical disc 100which allows only sequential recording, various recording statuses aremixed in the optical disc 100 which allows random recording. In thiscase, it is necessary to read the read signal R_(RF) in which thewaveform distortion is discontinuously or discretely distributed or notdistributed, or to read the read signal. R_(RF) which has various signallevels. Therefore, by reproducing the record data without correcting thewaveform distortion in a normal case, and by reproducing the record datawhile selectively correcting the waveform distortion in the case wherethe waveform distortion actually occurs, it is possible to receive theaforementioned various effects while reducing the load of theinformation reproducing apparatus 1.

(4-2) Second Modified Example

Firstly, with reference to FIG. 13 to FIG. 17, an informationreproducing apparatus 1 b in a second modified example will bedescribed. FIG. 13 is a timing chart conceptually showing an operationof correcting the waveform distortion by the information reproducingapparatus 1 b in the second modified example, on a first read signalR_(RF). FIG. 14 is a timing chart conceptually showing the operation ofcorrecting the waveform distortion by the information reproducingapparatus 1 b in the second modified example, on a second read signalR_(RF). FIG. 15 is a flowchart conceptually showing a first flow ofoperations by the information reproducing apparatus 1 b in the secondmodified example. FIG. 16 is a flowchart conceptually showing a secondflow of operations by the information reproducing apparatus 1 b in thesecond modified example. FIG. 17 is a flowchart conceptually showing athird flow of operations by the information reproducing apparatus 1 b inthe second modified example.

The record data recorded on the optical disc 100 includes not onlynormal user data but also the synchronization data (e.g. the record datawith a run length of 14T if the optical disc 100 is a DVD, and therecord data with a run length of 9T if the optical disc 100 is aBlue-ray Disc) used for synchronization in reproducing the user data. Inthe second modified example, considering that the synchronization datais included in the record data, the correction of the waveformdistortion may be limited to the synchronization data.

More specifically, as shown in FIG. 13, if the optical disc 100 is aBlu-ray Disc, since the synchronization data is formed of a 9T mark anda 9T space, firstly, the 9T space is detected, and the waveformdistortion before or after the detected 9T space may be corrected.Moreover, focusing on periodicity that the synchronization data appears,the waveform distortion may be corrected near a position being shiftedby a time corresponding to 1932T (or 1932T±α1: α1 is a predeterminedconstant) from the detected 9T space toward the advancing direction (ora position being shifted by β1T from the relevant position toward theadvancing direction: β1 is a predetermined constant).

Moreover, as shown in FIG. 14, if the optical disc 100 is a DVD, sincethe synchronization data is a 14T mark or a 14T space, firstly, the 14Tspace is detected, and the waveform distortion may be corrected near aposition being shifted by a time corresponding to 1488T (or 1488T±α2: α2is a predetermined constant) from the detected 14T space toward theadvancing direction (or a position being shifted by β2T from therelevant position toward the advancing direction: β2 is a predeterminedconstant).

A flow of the operations if the optical disc 100 is a Blu-ray Disc (afirst operational flow) will be described, with reference to FIG. 1

As shown in FIG. 15, firstly, the operation of reproducing data recordedon the optical disc 100 is performed (step S101).

In the reproduction operation, it is judged whether or not the 9T spaceis detected (step S401).

As a result of the judgment in the step S401, if it is judged that the9T space is not detected (the step S401: No), the operational flowreturns to the step S401 again, and the judgment operation of whether ornot the 9T space is detected is repeated.

On the other hand, as a result of the judgment in the step S401, if itis judged that the 9T space is detected (the step S401: Yes), then, itis judged whether or not the record data (in other words, the readsignal R_(RF)) immediately before or immediately after the 9T space isthe 9T mark (step S402).

As a result of the judgment in the step S402, if it is judged that therecord data immediately before or immediately after the 9T space is the9T mark (the step S402: Yes), the operations are ended without change.

On the other hand, as a result of the judgment in the step S402, if itis judged that the record data immediately before or immediately afterthe 9T space is not the 9T mark (the step S402: No), the waveformdistortion immediately before or immediately after the 9T space or nearthe both positions is corrected (step S404). The correction of thewaveform distortion in the step S404 is performed in the same manner asthe operations in the step S103 to the step 106 in FIG. 4.

Next, another flow of the operations if the optical disc 100 is aBlu-ray Disc (a second operational flow) will be described, withreference to FIG. 16.

As shown in FIG. 16, firstly, the operation of reproducing data recordedon the optical disc 100 is performed (step S101).

In the reproduction operation, it is judged whether or not the 9T spaceis detected (step S401).

As a result of the judgment in the step S401, if it is judged that the9T space is not detected (the step S401: No), the operational flowreturns to the step S401 again, and the judgment operation of whether ornot the 9T space is detected is repeated.

On the other hand, as a result of the judgment in the step S401, if itis judged that the 9T space is detected (the step S401: Yes), then, itis judged whether or not the record data at a position being shifted bya time corresponding to 1932T (or 1932±α1) from the detected 9T spacetoward the advancing direction (or a position being shifted by β1T fromthe relevant position toward the advancing direction) is the 9T mark(step S502).

As a result of the judgment in the step S502, if it is judged that therecord data at the position being shifted by the time corresponding to1932T (or 1932±α1) from the detected 9T space toward the advancingdirection (or the position being shifted by β1T from the relevantposition toward the advancing direction) is the 9T mark (the step S502:Yes), the operations are ended without change.

On the other hand, as a result of the judgment in the step S502, if itis judged that the record data at the position being shifted by the timecorresponding to 1932T (or 1932±α1) from the detected 9T space towardthe advancing direction (or the position being shifted by β1T from therelevant position toward the advancing direction) is not the 9T mark(the step S502: No), the waveform distortion is corrected near theposition being shifted by the time corresponding to 1932T (or 1932±α1)from the detected 9T space toward the advancing direction (or theposition being shifted by β1T from the relevant position toward theadvancing direction) (step S504).

Next, a flow of the operations if the optical disc 100 is a DVD (a thirdoperational flow) will be described, with reference to FIG. 17.

As shown in FIG. 17, firstly, the operation of reproducing data recordedon the optical disc 100 is performed (step S101).

In the reproduction operation, it is judged whether or not the 14T spaceis detected (step S601).

As a result of the judgment in the step S601, if it is judged that the14T space is not detected (the step S601: No), the operational flowreturns to the step S601 again, and the judgment operation of whether ornot the 14T space is detected is repeated.

On the other hand, as a result of the judgment in the step S601, if itis judged that the 14T space is detected (the step S601 Yes), then, itis judged whether or not the read signal R_(RF) at a position beingshifted by a time corresponding to 1488T (or 1488±α2) from the detected14T space toward the advancing direction (or a position being shifted byβ2T from the relevant position toward the advancing direction) is the14T mark or the 14T space (step S602).

As a result of the judgment in the step S602, if it is judged that theread signal R_(RF) at the position being shifted by the timecorresponding to 1488T (or 1488±α2) from the detected 14T space towardthe advancing direction (or a position being shifted by β2T from therelevant position toward the advancing direction) is the 14T mark or the14T space (the step S602: Yes), the operations are ended without change.

On the other hand, as a result of the judgment in the step S602, if itis judged that the read signal R_(RF) at the position being shifted bythe time corresponding to 1488T (or 1488±α2) from the detected 14T spacetoward the advancing direction (or a position being shifted by β2T fromthe relevant position toward the advancing direction) is not the 14Tmark or the 14T space (the step S602: No), the waveform distortion iscorrected near the position being shifted by the time corresponding to1488T (or 1488±α2) from the detected 14T space toward the advancingdirection (or a position being shifted by β2T from the relevant positiontoward the advancing direction) (step S604). The correction of thewaveform distortion in the step S604 is performed in the same manner asthe operations in the step S103 to the step 106 in FIG. 4.

As described above, by correcting the waveform distortion in view ofthat the synchronization data is included in the record data, it ispossible to preferably perform the high-frequency emphasis on thesynchronization data which is more important than the user data,resulting in the preferable reproduction of the synchronization data.This can further increase the stability of the reproduction operation.

(5) Influence on Path Metric Calculation in PR (1, 2, 2, 1) Method

Next, in the PR (1, 2, 2, 1) method explained with reference to FIG. 6,an influence of the waveform distortion with respect to the path metriccalculation in the PRML process will be described, for reference, withreference to FIG. 18 to FIG. 20. FIG. 18 are a state transition diagramin the PR (1, 2, 2, 1) method and a trellis diagram obtained bydeveloping the state transition diagram in a time axis direction. FIG.19 is a waveform diagram conceptually showing the operation ofcorrecting the waveform distortion, on the sample value series RS_(C),the operation being aimed at sample values included in a range between asample value located two after a first zero cross point and a samplevalue located two before a second zero cross point, if the PR (1, 2,2, 1) method is applied. FIG. 20 is a waveform diagram conceptuallyshowing the operation of correcting the waveform distortion, on thesample value series RS_(C), the operation being aimed at sample valuesincluded in a range between a sample value located one after the firstzero cross point and a sample value located one before the second zerocross point, if the PR (1, 2, 2, 1) method is applied.

Incidentally; in the explanation in FIG. 18 to FIG. 20, a Blu-ray Discis used as one specific example of the optical disc 100.

If the data pattern of the record data on the optical disc 100 isexpressed by three bits which are continuous with respect to a time axis(i.e. expressed by NRZI), the data is shown by six types of datapatterns of (0, 0, 0), (0, 0, 1), (1, 0, 0), (0, 1, 1), (1, 1, 0), and(1, 1, 1). Incidentally, here, the bit on the right side is a new bit onthe time axis (i.e. the newest input bit). In the state transitiondiagram in FIG. 18( a) and the trellis diagram in FIG. 18( b), the sixtypes of data patterns are defined as follows: (0, 0, 0) is defined asS000, (0, 0, 1) is defined as S001, (1, 0, 0) is defined as S100, (0,1, 1) is defined as S011, (1, 1, 0) is defined as S110, and (1, 1, 1) isdefined as S111. Here, in a Blu-ray Disc, the mark/space with theshortest run length has a mark/space length of 2T, there are no datapatterns of (1, 0, 1) and (0, 1, 0). Therefore, the data pattern of (0,0, 1) can be transit only to the data pattern of (0, 1, 1), and the datapattern of (1, 1, 0) can be transit only to the data pattern of (1, 0,0). In other words, S001 is limited to the state transition to S011, andS110 is limited to the state transition to S100. Thus, the statetransition diagram in the code state of the record data on the opticaldisc 100 and the trellis diagram are as shown in FIG. 18( a) and FIG.18( b), respectively.

An Euclidean distance between the sample value S(k) of the read signalon which partial-response-equalization using the PR (1, 2, 2, 1) methodis performed and ideal sample values in the PR (1, 2, 2, 1) method isreferred to as a branch metric (i.e. probability in the state transitionat each time point k). The branch metric is accumulated in a series ofroutes (paths), thus providing a path metric. The ideal sample values inthe PR (1, 2, 2, 1) method are the seven values of Ref_H, Ref_M, Ref_L,ZL, −Ref_L, −Ref_M, and −Ref_H, as shown using FIG. 6.

Here, the path metric value of the state S000(k) at the time point k isdefined PM000(k). The path metric value of the state S001(k) at the timepoint k is defined PM001(k). The path metric value of the state S100(k)at the time point k is defined PM100(k). The path metric value of thestate S011(k) at the time point k is defined PM011(k). The path metricvalue of the state S110(k) at the time point k is defined PM110(k). Thepath metric value of the state S111(k) at the time point k is definedPM111(k). At this time, each of PM000(k), PM001(k), PM100(k), PM011(k),PM110(k), and PM111(k) is expressed as follows.

PM111(k)=min(PM111(k−1)+(S(k)−Ref_(—) H)² , PM011(k−1)+(S(k)−Ref_(—)M)²)

PM110(k)=min(PM111(k−1)+(S(k)−Ref_(—) M)² , PM011(k−1)+(S(k)−Ref_(—)L)²)

PM011(k)=PM001(k−1)+(S(k)−ZL)²

PM100(k)=PM110(k−1)+(S(k)−ZL)²

PM001(k)=min(PM000(k−1)+(S(k)+Ref_(—) M)² , PM100(k−1)+(S(k)+Ref_(—)L)²)

PM000(k)=min(PM000(k−1)+(S(k)+Ref_(—) H)² , PM100(k−1)+(S(k)+Ref_(—)M)²),

wherein min(A, B) here is assumed to such a function that A is outputtedif A≦B and that B is outputted if A>B. In the trellis diagram shown inFIG. 18( b), on branches crossing in the state at the time point k, thebranch having a smaller path metric value is selected (in other words,merged). For example, in the state S000(k) at the time point k, a brancha from S100(k−1) and a branch b from S000(k−1) cross each other. Here, apath metric value a_pm of the branch a and a path metric value b_pm ofthe branch b are as follows.

a _(—) pm=PM000(k−1)+(S(k)+Ref_(—) H)²

b _(—) pm=PM100(k−1)+(S(k)+Ref_(—) M)²

The branch a is the branch metric when 0 is newly inputted next to thedata pattern (0, 0, 0). Thus, the path metric value is calculated fromthe square of a difference between S(k) and −Ref_H. For the datapatterns at a time point k−1 of the branch a, there are two considerabledata patterns: (0, 0, 0, 0) and (1, 0, 0, 0). Thus, the path of thebranch a from the time point k−1 to the time point k is either a1 or a2in FIG. 19.

The branch b is the branch metric when 0 is newly inputted next to thedata pattern (1, 0, 0). Thus, the path metric value is calculated fromthe square of a difference between S(k) and −Ref_M. Considering therestriction that in a Blu-ray Disc, the mark/space with the shortest runlength in a Blu-ray Disc has a mark/space length of 2T, the data patternat the time point k−1 of the branch b is (1, 1, 0, 0). If thecalculation in the PR (1, 2, 2, 1) method is performed on this datapattern, 1×1+1×2+0×2+0×1=3. Since an all T center level is set to ZL(zero level), 3=ZL. Therefore, the path of the branch b from the timepoint k−1 to the time point k is a path starting from ZL, as shown asbin FIG. 19.

In FIG. 19, S(k) is the path that it is correct to be −Ref_M, and S(k+1)to S(k+5) are the paths that they are correct to be e −Ref_H. Thus, asdescribed above, if the waveform distortion is corrected from the samplevalue S(k+1) located two after the first zero cross point, the pathmetric value of the branch b (i.e. a value obtained by squaring thedifference between S(k) and −Ref_M) is less than the path metric valueof the branch a (i.e. (i.e. a value obtained by squaring the differencebetween S(k) and −Ref_H), so that a probability of selecting the path ofthe branch b is higher.

On the other hand, as shown in FIG. 20, if the waveform distortion iscorrected from the sample value S(k) located one after the first zerocross point, the path metric value of the branch a is less than the pathmetric value of the branch b, so that a probability of selecting thepath of the branch a is higher. This is not preferable due to the higherprobability that the mark length after binarization by the PRML processis longer than the original mark length. Therefore, in order not to havean adverse effect on the PRML process, if the PRML (1, 2, 2, 1) methodis adopted, the operation of correcting the waveform distortion ispreferably performed, aimed at the sample values included in the rangebetween the sample value located two after the first zero cross pointand the sample value located two before the second zero cross point, asdescribed above.

Incidentally, FIG. 18 to FIG. 20 explains the example in the PR (1, 2,2, 1) method; however, obviously, the same explanation can be applied ineach method other than the PR (1, 2, 2, 1) method (e.g. a PR (C1, C21,C22, . . . , C2k, C1) method). This results in the conclusion that, inthe PR (C1, C21, C22, . . . , C2k, C1) method), it is preferable toperformed the operation of correcting the waveform distortion, aimed atample values included in the range between the sample value located(k+1)/2 after the first zero cross point and the sample value located(k+1)/2 before the second zero cross point, as described above.

Incidentally, the waveform distortion occurs generally due to thedispersion of the shape, length, and the like of the marks formed on therecording surface of the optical disc 100. Therefore, the waveformdistortion tends to occur in the recording type optical disc 100, suchas a DVD-R/RW, a DVD+R/RW, a DVD-RAM and a BD-R/RE. However, even in theread-only type optical disc 100, such as a DVD-ROM and a BD-ROM, thewaveform distortion occurs if the synchronization data formed of therelatively long mark is adjacent to each other in a tracking direction,as shown in FIG. 21. For the waveform distortion occurring in theread-only type optical disc 100, according to the informationreproducing apparatus 1 described above, the correction can bepreferably made, obviously.

The present invention is not limited to the aforementioned example, butvarious changes may be made, if desired, without departing from theessence or spirit of the invention which can be read from the claims andthe entire specification. An information reproducing apparatus andmethod, and a computer program, all of which involve such changes, arealso intended to be within the technical scope of the present invention.

1-18. (canceled)
 19. An information reproducing apparatus comprising: acorrecting device for correcting waveform distortion occurring in a readsignal corresponding to at least a long mark, of a read signal read froma recording medium; and a processing device for performing a PRML(Partial Response Maximum Likelihood) process on the read signal inwhich the waveform distortion is corrected, wherein said correctingdevice corrects the waveform distortion occurring in the read signalcorresponding to synchronization data, the synchronization data beingused to read user data included in record data, the synchronization databeing included in the record data.
 20. The information reproducingapparatus according to claim 19, wherein if the waveform distortionoccurs in a direction that a signal level increases, said correctingdevice corrects the waveform distortion by correcting a signal componentof the read signal which is less than or equal to a reference level andwhich is in a range that does not mislead a path metric selection in thePRML process.
 21. The information reproducing apparatus according toclaim 19, wherein if the waveform distortion occurs in a direction thata signal level reduces, said correcting device corrects the waveformdistortion by correcting a signal component of the read signal which isgreater than or equal to a reference level and which is in a range thatdoes not mislead a path metric selection in the PRML process.
 22. Theinformation reproducing apparatus according to claim 19, wherein if saidprocessing device adopts a PR (C1, C21, C22, . . . , C2k, C1) method,said correcting device corrects the waveform distortion by correcting asignal component between a sample value which appears (k+1)/2 after afirst reference cross point and a sample value which appears (k+1)/2before a second reference cross point located next to the firstreference cross point.
 23. The information reproducing apparatusaccording to claim 19, wherein if said processing device adopts a PR (1,2, 1) method, said correcting device corrects the waveform distortion bycorrecting a signal component between a sample value which appears oneafter a first reference cross point and a sample value which appears onebefore a second reference cross point located next to the firstreference cross point.
 24. The information reproducing apparatusaccording to claim 19, wherein if said processing device adopts a PR (1,2, 2, 1) method, said correcting device corrects the waveform distortionby correcting a signal component between a sample value which appearstwo after a first reference cross point and a sample value which appearstwo before a second reference cross point located next to the firstreference cross point.
 25. The information reproducing apparatusaccording to claim 19, wherein if said processing device adopts a PR (1,2, 2, 2, 1) method, said correcting device corrects the waveformdistortion by correcting a signal component between a sample value whichappears two after a first reference cross point and a sample value whichappears two before a second reference cross point located next to thefirst reference cross point.
 26. The information reproducing apparatusaccording to claim 19, wherein if said processing device adopts a PR (1,2, 2, 2, 2, 1) method, said correcting device corrects the waveformdistortion by correcting a signal component between a sample value whichappears three after a first reference cross point and a sample valuewhich appears three before a second reference cross point located nextto the first reference cross point.
 27. The information reproducingapparatus according to claim 19, wherein if the waveform distortionoccurs in a direction that a signal level increases, said correctingdevice corrects the signal level of the waveform distortion to apredicated minimum value in the PRML process.
 28. The informationreproducing apparatus according to claim 19, wherein if the waveformdistortion occurs in a direction that a signal level reduces, saidcorrecting device corrects the signal level of the waveform distortionto a predicated maximum value in the PRML process.
 29. The informationreproducing apparatus according to claim 19, further comprising adetecting device for detecting the waveform distortion, said correctingdevice correcting the waveform distortion if the waveform distortion isdetected by said detecting device.
 30. The information reproducingapparatus according to claim 19, wherein said correcting device correctsthe waveform distortion (i) if an error correction of the read signalcannot be performed, (ii) if an error rate of the read signal is greaterthan or equal to a predetermined threshold value, or (iii) if a readsignal corresponding to synchronization data cannot be read, thesynchronization data being used to read user data included in recorddata, the synchronization data being included in the record data. 31.The information reproducing apparatus according to claim 19, whereinsaid correcting device corrects the waveform distortion at least one ofbefore a space which makes a pair with a mark which constitutes thesynchronization data of the read signal, after the space, and at aposition which satisfies periodicity of the synchronization data with abase point at the space.
 32. The information reproducing apparatusaccording to claim 19, wherein the long mark is a mark whose signallevel is maximum amplitude.
 33. The information reproducing apparatusaccording to claim 19, wherein said processing device comprises: anequalizing device for partial-response equalizing the read signal on thebasis of intentional waveform interference which can limit an areafrequency component included in the read signal; and a MaximumLikelihood decoding device for estimating a most probable series withrespect to an output of said equalizing device.
 34. An informationreproducing method comprising: a correcting process of correctingwaveform distortion occurring in a read signal corresponding to at leasta long mark, of a read signal read from a recording medium; and aprocessing process of performing a PRML (Partial Response MaximumLikelihood) process on the read signal in which the waveform distortionis corrected, wherein said correcting process corrects the waveformdistortion occurring in the read signal corresponding to synchronizationdata, the synchronization data being used to read user data included inrecord data, the synchronization data being included in the record data.35. A computer readable recording medium recording thereon a computerprogram for reproduction control and for controlling a computer providedin an information reproducing apparatus comprising: a correcting devicefor correcting waveform distortion occurring in a read signalcorresponding to at least a long mark, of a read signal read from arecording medium; and a processing device for performing a PRML (PartialResponse Maximum Likelihood) process on the read signal in which thewaveform distortion is corrected, wherein said correcting devicecorrects the waveform distortion occurring in the read signalcorresponding to synchronization data, the synchronization data beingused to read user data included in record data, the synchronization databeing included in the record data, said computer program making thecomputer function as at least one portion of said correcting device andsaid processing device.